1. Field of the Invention
The present invention relates to a heat-resistant alloy member in which the surface of an alloy member containing Cr is coated with a Cr diffusion preventing layer, an alloy member for a fuel cell, a collector member for a fuel cell, a cell stack, and a cell apparatus.
2. Description of the Related Art
As a next-generation energy system, for example, various fuel cell apparatuses comprising a container and a cell stack of fuel cells housed in the container have recently been proposed. A solid electrolyte fuel cell is formed by housing a cell stack comprising plural fuel cell cells, which are electrically connected to each other, in a container. A fuel gas (hydrogen) is allowed to flow to the side of a fuel electrode of a fuel cell and air (oxygen) is allowed to flow to the side of an air electrode (also referred to as an oxygen electrode) thereby generating power at a high temperature of 550 to 900° C. A felt- or plate-like collector member has conventionally been used so as to electrically connect between fuel cells.
An alloy having high conductivity is employed as the collector member and also a heat-resistant alloy is preferably employed since it is used at a high temperature. As the heat-resistant alloy having high conductivity, an alloy containing 10 to 30% by mass of Cr is usually employed. However, when a collector member made of an alloy containing Cr is interposed between fuel cells thereby electrically connecting plural fuel cells to each other, Cr in the collector member diffuses out from the collector member during power generation of the fuel cell for a long period and the diffused Cr reaches the interface between the air electrode and the solid electrolyte, resulting in deterioration of activity. This phenomenon is so-called Cr poisoning and causes deterioration of power generation ability of the fuel cell.
The surface of an alloy member containing Cr has conventionally been coated with Mn, Fe, Co or Ni so as to prevent the Cr poisoning (refer to Kohyo (National Publication of Translated Version) No. 11-501764).
However, when the surface of a Cr-containing alloy member is coated with Mn, Fe, Co or Ni as described in Kohyo (National Publication of Translated Version) No. 11-501764, Cr still diffuses drastically, although it is possible to suppress Cr in the Cr-containing alloy member from diffusing out to some extent.